CP violation in t → W + b decays in two-Higgs doublet model

Due to the large mass of top quark, CP violation in the top-quark decay is sensitive to the interactions mediated by Higgs bosons. We consider CP violation in t → W ⁺ b decay by calculating consistently in unitary gauge the CP-violating up-down asymmetry of the leptons from W boson decays in t → W ⁺ b, defined by Grz?dkowski and Gunion, in the two-Higgs doublet model with CP-violating neutral sector. The asymmetry is shown to be at most of the order of (1–4) × 10^-4 for tan β = 1.0, where tan β is the ratio of vacuum expectation values for the two neutral Higgs bosons.     

First observation of a particle-antiparticle asymmetry in the decay of neutral kaons into π0π0

CP violation has been observed as a time-dependent rate asymmetry between the decays ${?erline K}^0 ?ghtarrow ?^{0} ?^{0}$ and K⁰ → π⁰π{0}, where the neutral kaons are produced with definite and individually known strangeness in ${?r p}p ?ghtarrow{?erline K}^0 K^+?^- $ or p?p → K⁰ K^? π⁺. A special technique for the data analysis has been developed. The values obtained for ?₀₀ and ¦ η₀₀¦ are in agreement with those of previous measurements of CP violation.     

Measurement of inclusive π0 production in hadronic Z 0 decays

An analysis is presented of inclusive π⁰ production in Z ⁰ decays measured with the DELPHI detector. At low energies, π⁰ decays are reconstructed by using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to $x_p={2cdot p?/{sqrt s}=0.75}$) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for qq? and bb? events. The number of π⁰’s per hadronic Z ⁰ event is $N(?^0)/Z_{had} ^0=9.2pm 0.2({? stat})pm 1.0 ({? syst})$ and for bb? events the number of π⁰’s is ${? N}(?^0)/{? b?r b}=10.1pm 0.4({? stat})pm 1.1 ({? syst})$. The ratio of the number of π⁰’s in bb? events to hadronic Z ⁰ events is less affected by the systematic errors and is found to be 1.09 ±0.05 ±0.01. The measured π⁰ cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in the $xi_{? p}={? ln}(1/{? x_p})$ distribution is $xi_p^{?ar}=3.90_{-0.14}^{+0.24}.$ The average number of π⁰’s from the decay of primary B hadrons is found to be N(B → π⁰ X)/B hadron = 2.78 ± 0.15(stat) ± 0.60(syst).     

Measurement of $D_s ^+$ meson production in Z decays and of the ${⋏r B}_s ^0$ lifetime

$D_s ^+$ mesons produced in Z⁰ → bb? events were separated from the Z⁰ → cc? component using a lifetime tag. Using a sample of 1.5 million hadronic Z decays collected with the Aleph detector the ${?r B}_s ^0$ and $D_s ^+$ yields have been measured: $$?trix {B(b?ghtarrow {?r B}_s ^0)B({?r B}_s ^0?ghtarrow D_s ^+)=0.088pm 0.020(? stat.)? pm 0.020(? syst.)? B(c?ghtarrow D_s ^+)=0.128pm 0.019(? stat.)_{-0.016} ^{+0.019}(? syst.)}$$ The ${?r B}_s ^0$ lifetime was measured in a ${?r B}_s ^0$ enriched sample reconstructing the decay length from the vertex of the $D_s ^+$ with a hadron from the ${?r B}_s ^0$ decay. The result obtained is: $${?u_B}_s=1.61_{-0.29} ^{+0.30}(? stat.)_{-0.16} ^{+0.18}(? syst.) {? ps.}$$     

An improved measurement of R b using a double tagging method

This paper describes an update of the double tagging measurement of the fraction, R _b, of Z⁰ → bb? events in hadronic Z⁰ decays, with statistics improved by including the data collected in 1994. The presence of electrons or muons from semileptonic decays of bottom hadrons and the detection of bottom hadron decay vertices were used together to obtain an event sample enriched in Z⁰ → bb? decays. The efficiency of the bb? event tagging was obtained from the data by comparing the numbers of events having a bottom signature in either one or both thrust hemispheres. Efficiency correlations between opposite event hemispheres are small (< 0.5%) and well understood through comparisons between the real and simulated data samples. A value of R _b = 0.2175 ± 0.0014 ± 0.0017 was obtained, where the first error is statistical and the second systematic. The uncertainty on the decay width Γ(Z⁰ → cc?) is not included in these errors. The result depends on R _c as follows: $${? Delta R_{? b}?er R_{? b}}=-0.084{? Delta R_{? c}?er R_{? c}},$$ where ΔR _c is the deviation of R _c from the value 0.172 predicted by the Standard Model.     

Study of the CP-violating effects with <Emphasis Type="Italic">gg</Emphasis> → <Emphasis Type="Italic">Η</Emphasis> → τ<Superscript>+</Superscript>τ<Superscript>–</Superscript> process

Study of the gg → Η → τ⁺τ^– process was performed at Monte Carlo level within the framework of searching for CP-violating effects. The sensitivity of chosen observables to CP-parity of the Higgs boson was demonstrated for hadronic 1-prong τ decays (τ^± → π^±, ρ^±). Monte Carlo samples for the gg → Η → τ⁺τ^- process were generated including the parton hadronisation to final state particles. This generation was performed for the Standard Model Higgs boson, the pseudoscalar Higgs boson, the Z → τ⁺τ^– background, and mixed CP-states of the Higgs boson.     

Search for CP violation in D± meson decays to ϕπ±

We search for CP violation in Cabibbo-suppressed charged D meson decays by measuring the difference between the CP-violating asymmetries for the Cabibbo-suppressed decays D(±)→K(+)K(-)π(±) and the Cabibbo-favored decays D(s)(±)→K(+)K(-)π(±) in the K(+)K(-) mass region of the ? resonance. Using 955 fb(-1) of data collected with the Belle detector, we obtain A(CP)(D+→?π+)=(+0.51±0.28±0.05)%. The measurement improves the sensitivity of previous searches by more than a factor of 5. We find no evidence for direct CP violation.     

CP noninvariance and the possibility of a sizable neutron electric dipole moment

The electric dipole moment of the neutron will be measured to a precision of 10^?25 e-cm in the near future. We explore a new theoretical possibility that P and CP noninvariance leads to a sizable electric dipole moment. We calculate an electric dipole moment of about 10^?25 e-cm. In this phenomenological theory, we calculate CP-violating observables in non-leptonic decays from theK ⁰ ? \(\bar K^0 \) ,Λ ⁰ ?Λ ⁰ andK ⁺?K ^? systems. In connection with CP noninvariance, the possible observable occurrence of ΔS=2 decays is discussed. We calculate possible branching ratios; in particular that forΞ ⁰ → π^? p can be as high as about 10^?6. The possible existence of a weakly interacting, neutral scalar boson, which violates P and CP in the course of its propagation as a virtual particle, is considered.     

The Z → c \bar c → γγ*, Z → b \bar b → γγ* triangle diagrams and the Z → γψ, Z → γϒ decays

The approach to the Z → γψ and Z → γ? decay study is presented in detail, based on the sum rules for the Z → c $ \bar c $ → γγ* and Z → b $ \bar b $ → γγ* amplitudes and their derivatives. The branching ratios of the Z → γψ and Z → γ? decays are calculated for different hypotheses on saturation of the sum rules. The lower bounds of Σ _ψ BR(Z → γψ) = 1.95 × 10^?7 and Σ_υ BR(Z → γ?) = 7.23 × 10^?7 are found. Deviations from the lower bounds are discussed, including the possibility of BR(Z → γJ/ψ(1S)) ～ BR(Z → γ?(1S)) ～ 10^?6, that could be probably measured in LHC. The angular distributions in the Z → γψ and Z → γ? decays are also calculated.     

Single decay-lepton angular distributions in polarizede + e − →\overline {tt} and simple angular asymmetries as a measure of CP-violating top dipole couplingsand simple angular asymmetries as a measure of CP-violating top dipole couplings

In the presence of an electric dipole coupling of $\overline {tt} $ to a photon, and an analogous ‘weak’ dipole coupling to the Z, CP violation in the process e⁺e^? → $\overline {tt} $ results in modified polarization of the top and the anti-top. This polarization can be analyzed by studying the angular distributions of decay charged leptons when the top or anti-top decays leptonically. Analytic expressions are presented for these distributions when eithert or $\overline t $ decays leptonically, including $\mathcal{O}$ (α_s) QCD corrections in the soft-gluon approximation. The angular distributions are insensitive to anomalous interactions in top decay. Two types of simple CP-violating polar-angle asymmetries and two azimuthal asymmetries, which do not need the full reconstruction of thet or $\overline t $ , are studied. Independent 90% CL limits that may be obtained on the real and imaginary parts of the electric and weak dipole couplings at a linear collider operating at √ s = 500 GeV with integrated luminosity 500 fb^? and also at √s = 1000 GeV with integrated luminosity 1000 fb^? have been evaluated. The effect of longitudinal electron and/or positron beam polarizations has been included.     

Decays of a neutral particle with zero spin and arbitrary CP parity into two off-mass-shell <Emphasis Type="Italic">Z</Emphasis> bosons

We investigate effects of CP symmetry violation in the decay of a scalar particle X (the Higgs boson) into two off-mass-shell Z bosons both decaying into a fermion–antifermion pair, \(X \to {Z_1}*{Z_2}* \to {f_1}{\bar f_1}{f_2}{\bar f_2}\). The most general form of the amplitude of the transition X → Z₁*Z₂*, wherein the boson X may not have definite CP parity, is considered. The applicability limits of the narrow-Z-width approximation used in obtaining differential widths of the decay under consideration are determined. Various observables connected with the structure of the amplitude of the decay X → Z₁*Z₂* are studied. These observables are analyzed in the Standard Model as well as in models conceding indefinite CP parity of the Higgs boson. An experimental measurement of angular and invariant mass distributions of the decay \(X \to {Z_1}*{Z_2}* \to {f_1}{\bar f_1}{f_2}{\bar f_2}\) at the LHC can give information about the CP properties of the Higgs boson and its interaction with the Z boson.     

MSSM Higgs searches in multi-b-jet final states at the LHC

This paper discusses the possibility to observe a signal from MSSM Higgs boson decays into final states containing four b-jets. Two specific channels are considered: bb?H and bb?A production with H,A → bb?, for large values of m_H, m_A and tan β, and H → hh → bb?bb? decays for 150 GeV < m_H < 2m_t and for low values of tan β. Both channels are difficult to extract because of the very large reducible and irreducible QCD backgrounds. Even with an ultimate integrated luminosity, expected per LHC experiment, of 3 · 10⁵ pb^-1, the region of the MSSM parameter space covered by these channels does not extend the reach beyond that accessible to other channels that were studied in the past. Nevertheless, their observation would help in constraining the couplings and branching ratios of the MSSM Higgs bosons.     

CP violation in a multi higgs doublet model

We study CP violation in a multi-Higgs doublet model based on aS ₃×Z ₃ horizontal symmetry. We consider two mechanisms for CP violation in this model: a) CP violation due to complex Yukawa couplings; and b) CP violation due to scalarpseudoscalar mixings. We find that the predictions for ε′/ε, CP violation in B decays and the electric dipole moments of neutron and electron are different between these two mechanisms. These predictions are also dramatically different from the minimal Standard Model predictions.     

CP violation and the widthZ→b \bar b

We discuss the effect of CP-violatingZb $\bar b$ Zb $\bar b$ G andZb $\bar b$ γ couplings on the width Γ(Z→b $\bar b$ X). The presence of such couplings leads in a natural way to an increase of this width relative to the prediction of the standard model. Various strategies of a direct search for such CP-violating couplings by using CP-odd observables are outlined. The number ofZ bosons required to obtain significant information on the couplings in this way is well within the reach of present LEP experiments.     

A constraint from B decay on models with no t quark

We show that if the b quark is assigned to a singlet representation of the weak interaction SU(2) symmetry and if it decays through the usual weak bosons W^± and Z⁰, then neutral current decays occur at such a rate that Λ(B→X?⁺?^?)/Λ(B→X?⁺ν)?0.12, even allowing arbitrarily many quarks with which the b can mix. We discuss the manner in which the experimental exlusion of this inequality would constrain the possibilities for t-free models.     

The process e + e − → bb̅W + W − at the next linear collider in the Minimal Supersymmetric Standard Model

The complete matrix element for e ⁺ e^? → bb?W⁺ W^? is computed at tree-level within the Minimal Supersymmetric Standard Model. Rates of interest to phenomenological analyses at the Next Linear Collider are given. In particular, we study:

• ? tt? production and decay tt? →(bW ⁺)(b?W ^?)
• ? ZH production followed by Z → bb? and H → W ⁺ W^?
• ? AH production followed by A→ bb? and H → W ⁺ W^?
• ? hW ⁺ W^? production followed by h→ bb?.

Top and Higgs finite width effects are included, as well as all those of the irreducible backgrounds.     

Search for lepton flavour number violating Z0- decays

A search for lepton flavour number violating Z⁰ decays in the channels Z ⁰ → μτ, Z ⁰ → eτ, Z ⁰ → eμ, using the DELPHI detector with data collected during the 1991–94 LEP runs, is described. No signal was found. Upper limits at 95% confidence level for the respective branching fractions of 1.2 × 10^?5, 2.2 × 10^?5, and 0.25 × 10^?5, were obtained.     

Search for ξ(2.2) andX(2.2) in radiative decays of ϒ-meson

The results of an experiment on the search for ξ(2.2) andX(2.2) in the radiative decays of the Υ-meson are presented. The experiment was carried out with the MD-1 detector at the VEPP-4 collider. An upper limitB(Υ→γξ)B(ξ→K ⁺ K ^?)<2·10^?4 is obtained at 90% C.L. Results are presented on the search for the decay Υ→γX, X→ ?? not previously investigated. For this decay the upper limitB(Υ→γX)B(X→??)<3·10^?3 is obtained at 90% C.L.     

Direct CP violation in B(-/+) --> ppK((*)+/-)

We study the direct CP violation in B(-/+) --> ppK((*)+/-) decays in the standard model. We point out that these three-body baryonic B decays can be important tools for detecting the direct CP violation in the charged B system, in which there are no conclusive signatures yet. In particular, we show that the direct CP-violating asymmetry in B(-/+) --> ppK((*)+/-) is around 22%, which supports the recent data by the BABAR Collaboration.     

CP violation and strong phases from penguins in B±→PP and B±→VP decays

We calculate direct CP-violating rate asymmetries in chargedB→PP andB→VP decays arising from the interference of amplitudes with different strong and CKM phases. The perturbative strong phases develop at order α _s from absorptive parts of one-loop matrix elements of the next-to-leading logarithm corrected effective Hamiltonian. CPT constraints are maintained. Based on this model, we find that partial rate asymmetries between charge conjugateB ^± decays can be as high as 20% for certain channels with branching ratios in the 10^?6 range. Because the $c\bar c$ threshold lies so close to the physical momentum scale, the asymmetries depend sensitively on the model assumptions used to evaluate the imaginary parts of the matrix elements, in particular, on the internal momentum transfer. The charge asymmetries of partial rates would provide unambiguous evidence for direct CP violation.